Compounds having cytotoxicity have been used as antitumor agents, and many screenings have been carried out using cytotoxicity as an index. As a result, most of pre-existing antitumor agents give affection to cancer cells and simultaneously to normal tissues in which a proliferation of cell is active, for example, to bone marrow, intestine epithelium and the like. Thus, the improvement of QOL of patients has not been sufficiently accomplished yet.
Further, although it can be expected that treatments by the antitumor agents are rather effective for leukemia, it cannot be always said that they are effective for solid cancer. Therefore strong demands have been made to provide antitumor agents that are effective for solid cancer and are highly safe.
Screenings for fermentation products of microorganism have been carried out using the cytotoxicity in vitro as an index, expecting that they might also be used as antitumor agents. Many compounds having cytotoxicity have been found, however, most of them show cytotoxic activities only in vitro, and few compounds of them show antitumor activities in vivo, and very few compounds exhibit effectiveness for solid cancer.